U.S. Pat. No. 6,286,535 B1 discloses a proportional pressure-regulating valve conforming to its genre, having a pump port axially disposed in relation to the direction of displacement of a regulating piston within a valve housing. Fluid-conducting connections such as a utility port and a tank port are discharged transversely to the axial direction of displacement of the regulating piston into the valve housing and into an annular space delimited on one side by the valve housing, and on the other side by the regulating piston. Disposed in an axial direction between one end of the regulating piston and the valve housing is a damping chamber that is always connected with this annular space in a fluid-conducting manner by an aperture such that movements of the regulating piston in the valve housing are damped by the compensation device formed by the aperture. The proportional pressure-regulating valve disclosed shown is therefore able to significantly dampen sudden changes in the volumetric flow rate in terms of the effect of those changes on the hydraulic pilot control of the proportional pressure-regulating valve, for example in the case of a hydraulically controlled coupling or a similar load.
DE 44 42 085 C2 discloses an electromagnetically actuated proportional pressure-regulating valve having:                a valve body having at least one fluid inlet opening and one fluid outlet opening as well as a channel connecting the fluid inlet opening with the fluid outlet opening;        a valve piston housed in the valve body and disposed between the fluid inlet opening and the fluid outlet opening such that that piston can be actuated to open and close the channel, with the valve piston having a bore with a reduced diameter;        a piston disposed and enclosed in the valve body to form a pressure chamber, with the piston having a pilot valve disposed outside of the pressure chamber and with the pilot valve disposed such that it can be actuated to regulate the pressure in the pressure chamber;        a return channel formed by the piston between the pressure chamber and the fluid outlet opening; and        an electrical device having an electromagnetic coil and a core composed of a material generating an electromagnetic force to move the pilot valve of the piston.        
U.S. Pat. No. 5,836,335 discloses a proportional pressure-regulating valve, in which a regulating piston has a device for limiting pressure peaks such as can occur at a load port of a load for actuating a hydraulically actuated coupling, for example.
To that end, in the case of a preferred embodiment of the known valve, a spring-loaded check valve is used in the regulating piston, which check valve can be connected to the load port by an annular space. A pressure threshold value can be predetermined for the proportional pressure-regulating valve to the effect that, in the case that the pressure threshold value is exceeded, a fluid-conducting connection between the annular space and a circumferential groove in the regulating piston is released. The annular space is constantly connected to a tank port.
In particular in the case of hydraulic actuators used to actuate clutches in a drive train, it is desirable to fill or drain their working chambers with pressurizing medium. In particular, a horizontal p-Q characteristic of the proportional pressure-regulating valves used to control the flow of pressurizing medium for the hydraulic actuators is advantageous. The known proportional pressure-regulating valves are affected with respect to their control behavior of the volumetric flow rate.